US6200477B1 - Continuously regenerated and integrated suppressor and detector for suppressed ion chromatography and method - Google Patents

Abstract

An integrated suppressor and detector for suppressed ion chromatography includes a stationary phase, a fluid flow path, at least first and second regeneration electrodes, and at least first and second sensor electrodes. Methods of suppressed ion chromatography using the integrated suppressor and detector are also described.

Description

FIELD OF THE INVENTION

The present invention relates to the field of ion chromatography (IC), and, in particular, to a continuously regenerated, integrated suppressor and detector for use in suppressed ion chromatography (SIC).

BACKGROUND OF THE INVENTION

Suppressed ion chromatography (SIC) is a commonly practiced method of ion chromatography which generally uses two ion-exchange columns in series followed by a flow through conductivity detector for detecting sample ions. The first column, called the analytical or separation column, separates the analyte ions in a sample by elution of the analyte ions through the column. The analyte ions are flowed through the analytical column via a mobile phase comprising electrolyte. Generally, a dilute acid or base in deionized water is used as the mobile phase. From the analytical column, the separated analyte ions and mobile phase are then flowed to the second column, which is called the suppressor or stripper. The suppressor serves two primary purposes: (1) it lowers the background conductance of the mobile phase by retaining (e.g., suppressing) the electrolyte of the mobile phase, and (2) it enhances the conductance of the analyte ions by converting the analyte ions to their relatively more conductive acid (in anion analysis) or base (in cation analysis). The combination of these two functions enhances the signal to noise ratio, and, thus, improves the detection of the analyte ions in the detector. Accordingly, upon exiting the suppressor, the analyte ions and suppressed mobile phase are then flowed to the detector for detection of the analyte ions. A variety of different types of suppressor devices and methods are discussed in U.S. Pat. Nos. 3,897,213; 3,920,397; 3,925,019; 3,926,559; and U.S. Ser. No. 08/911,847. Applicants hereby incorporate by reference the entire disclosure of these patent applications and patents.

As those skilled in the art will appreciate, both the mobile phase and the sample contain counterions of the analyte ions. A suppressor operates by ion exchange of suppressor ions, which are located in the suppressor, with both the (1) the mobile phase electrolyte counterions and (2) the sample counterions. In anion analysis, for example, the suppressor ions normally comprise hydronium ions and the mobile phase comprises electrolyte such as sodium hydroxide or mixtures of sodium carbonate and sodium bicarbonate. In cation analysis, the suppressor ions normally comprise hydroxide ions, and the mobile phase may comprise electrolytes such as hydrochloric acid or methanesulfonic acid. The suppressor ions are located on a stationary phase, which may be an ion exchange membrane or resin. As the mobile phase and sample (which contains both analyte ions and counterions of the analyte ions) are flowed through the stationary phase of the suppressor, the electrolyte counterions in the mobile phase and the sample counterions are retained on the stationary phase by ion exchange with the suppressor ions. When the suppressor ions are either hydronium or hydroxide, ion exchange of the electrolyte counterions with suppressor ions converts the mobile phase to water or carbonic acid, which are relatively non-conductive. On the other hand, the ion exchange of sample counterions with suppressor ions (i.e., hydronium or hydroxide ions) converts the analyte ions to their relatively more conductive acid (in anion analysis) or base (in cation analysis). Thus, the analyte ions, which are now in their relatively more conductive acid or base form, are more sensitive to detection against the less conductive background of the mobile phase.

However, unless the suppressor ions are continuously replenished during the suppression process, the concentration of suppressor ions on the stationary phase is reduced. Eventually the suppressor will become exhausted and its suppression capacity is either lost completely or significantly reduced. Thus, the suppressor must be either replaced or regenerated. The need to replace or regenerate the suppressor is inconvenient, may require an interruption in sample analysis, or require complex valving or regeneration techniques known in the art. One example of a known technique for regenerating a suppressor by continuously replenishing suppressor ions is disclosed in U.S. Pat. No. 5,352,360.

In addition to the need for regenerating or replacing suppressor ions, another problem associated with SIC is that a separate suppressor unit is usually required, and, therefore, the number of components in the system is increased over traditional IC systems. Traditional IC systems usually contain a mobile phase source, a pump, a sample injector, an analytical column and a detector for detecting the sample ions. In SIC, a separate suppressor unit is added to the system. This, in turn, increases the complexity of the system and also increases extra-column volume which may decrease chromatographic resolution and sensitivity. Therefore, it would also be advantageous to have a system of ion suppression chromatography which reduced the number of system components in traditional SIC systems.

Another problem associated with prior art SIC systems is that the mobile phase is converted to a weakly ionized form, which renders the mobile phase unsuitable for reuse. Thus, it would be advantageous if a system of SIC were developed in which the mobile phase is converted back to its strongly ionized form after suppression and, thus, may be reused.

SUMMARY OF THE INVENTION

In its various aspects, the present invention is capable of solving one or more of the foregoing problems associated with SIC.

In one aspect of the present invention, an integrated suppressor and detector is provided. By “suppressor” it is meant a device that is capable of converting the mobile phase to water or a weakly conductive form such as, for example, sodium carbonate or bicarbonate to carbonic acid and the ions to be detected (e.g. the analyte ions) to either their acid or base prior to detection. In this aspect of the invention, the suppressor is further equipped with sensor electrodes for detecting the analyte ions. By “integrated” it is meant that the suppressor and detector are contained within the same housing so that fluid transfer lines between a separately housed suppressor and detector are unnecessary.

In a further aspect of the invention, a method of suppression ion chromatography is provided wherein the suppressor is continuously regenerated during suppression. The suppressor comprises a stationary phase comprising suppressor ions which acts to suppress a mobile phase containing analyte ions to be detected. Electrolysis is performed on the mobile phase to produce regenerating ions. The regenerating ions are then flowed through the stationary phase to continuously replenish the suppressor ions lost during suppression. Preferably, electrolysis is performed on water present in the mobile phase.

In another aspect of the invention, an integrated suppressor and detector is provided. The integrated suppressor and detector comprises at least first and second regeneration electrodes and a fluid flow path extending between the first and second regeneration electrodes. A stationary phase comprising suppressor ions is positioned in the fluid flow path. The integrated suppressor and detector further comprises at least first and second sensor electrodes, in an electrical communication with a measuring device for recording analyte ions detected by the sensor electrodes.

In yet another aspect of the invention, a method of suppression ion chromatography is provided wherein the suppressed mobile phase is converted back to its strongly ionized state after suppression. Thus, the mobile phase is recycled and may be reused.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a suppressor ion chromatography system incorporating the integrated suppressor and detector of the invention.

FIG. 2 is a cross-section view of integrated suppressor and detector according to one aspect of the invention taken alongline2—2 of FIG. 3a.

FIG. 3ais a side perspective view of an integrated suppressor and detector according to one aspect of the invention.

FIG. 3bis a cross-section view taken along line B—B of FIG. 3a.

FIG. 4 is an exploded perspective view of an integrated suppressor and detector according to another aspect of the invention.

FIG. 4ais a side view of an integrated suppressor and detector depicted in FIG.4.

FIG. 4bis a cross-sectional view of an integrated suppressor and detector.

FIGS. 5-7 are chromatograms using an apparatus and method according to the invention and are referred to in the examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates an IC system using the integrated suppressor and detector of the present invention. The IC system comprises amobile phase source10, apump11, asample injector12 and ananalytical column14, all in fluid communication. Thepump11,sample injector12 andanalytical column14 may be selected from the variety of types known by those skilled in the art For example, preferred pumps include the ALLTECH 526 pump available from ALLTECH ASSOCIATES, INC. (Deerfield, Ill.). Preferred analytical columns include the ALLTECH ALLSEP or UNIVERSAL CATION COLUMNS. Preferred sample injectors include the RHEODYNE 7725 injection valve.

An integrated suppressor anddetector16 in fluid communication with theanalytical column14 is further provided. As discussed below, the suppressor anddetector16 is connected to apower source18 and a measuringdevice20. Preferred power sources include the KENWOOD PR36-1.2A. A preferred measuring device is a conductivity detector such as the OAKTON ¼ DIN Conductivity and Resistivity Controllers (OAKTON 100 Series). Another suitable measuring device for use with the present invention is an electrochemical detector. The measuringdevice20 measures or records the analyte ions detected by sensor electrodes in the integrated suppressor anddetector16.

In operation, the direction of fluid flow is as follows. The mobile phase is flowed frommobile phase source10 bypump11 throughinjection valve12 toanalytical column14 to suppressor anddetector16. Upon exiting the suppressor anddetector16, the mobile phase is flowed throughrecycling valve19, which directs fluid flow either to waste or back tomobile phase source10 as discussed below. Therecycling valve19 is preferably a three-way valve.

With reference to FIG. 2, the suppressor anddetector16 comprises afirst regeneration electrode30 and asecond regeneration electrode32. The regeneration electrodes are held inhousing17 of the suppressor anddetector16 by a threaded nut (not shown).Seals241 and241aare preferably included to provide a fluid-tight seal betweenelectrodes30 and32 andhousing17. Theseals241 and241aare preferably O-rings made from materials that are compatible with acids and bases such as, for example, ethylene propylene. Preferably, the regeneration electrodes are flow-through electrodes. By flow-through electrodes, it is meant that the electrodes allow sample analyte ions and mobile phase to flow therethrough. The electrodes are preferably made from carbon, platinum, titanium, stainless steel or any other suitable conductive, non-rusting material. The most preferred electrodes are made of platinum coated titanium, ruthenium oxide coated titanium, titanium nitride coated titanium, gold, or rhodium with an average pore size of between 0.1 μm and 100 μm. Thefirst regeneration electrode30 and thesecond regeneration electrode32 are connected to thepower source18. A fluid flow path (indicated by arrows) is positioned between the first and second regeneration electrodes. The fluid flow path may preferably extend from thefirst regeneration electrode30 to thesecond regeneration electrode32. The fluid flow path may be defined by internal walls ofhousing17.Housing17 is preferably made from an inert material such as those disclosed in co-pending application Ser. No. 08/911,847. Also, as those skilled in the art will appreciate, thehousing17 should be constructed from a relatively non-conductive material.

Astationary phase39 is positioned in the fluid flow path. Thestationary phase39 may comprise a variety of stationary phases known in the art for suppressors. Such stationary phases include membranes and ion exchange resins, for example. Preferably, the stationary phase comprises ion exchange resin. In anion analysis, cation exchange resin will be used. A preferred cation exchange resin is BIORAD AMINEX 50W-X12 (which is a sulfonated polystyrene divinylbenzene 200-400 mesh). Other suitable stationary phases include DUPONT NAFION ion-exchange beads and membranes and PUROLITE ion-exchange resins. During operation, the preferred cation exchange resin comprises exchangeable hydronium ions. In cation analysis, anion exchange resin will be used. A preferred anion exchange resin is BIORAD AMINEX AG1-X8 100-200 mesh (which is a quaternary amine polystyrene divinyl benzene). During operation, the preferred anion exchange resin comprises exchangeable hydroxide ions.

The suppressor anddetector16 also comprise at least two sensor electrodes for detecting the analyte ions. In the present embodiment, two sensor electrodes,first sensor electrode37 andsecond sensor electrode38 are shown. The first and second sensor electrodes are preferably located in the fluid flow path betweenfirst regeneration electrode30 andsecond regeneration electrode32. The first and second sensor electrodes preferably comprise either platinum wire or another electrochemically inert material such as gold, rheuthinium oxide or platinum, either neat or plated or suitable substrates such as titanium or stainless steel. Thesensor electrodes37 and38 are preferably in electrical communication with a measuring device (not shown) for recording the analyte ions detected by the sensor electrodes. With reference to FIGS. 3aand3b,the first and second sensor electrodes preferably have a serpentine configuration across a cross-section of the flow path. In particular, two rows of four holes each (see reference numerals40-43 and44-47, respectively) are provided. Thefirst sensor electrode37 is weaved through holes40-43 and thesecond electrode38 is weaved through holes44-47 formed inhousing17. Most preferably, at least a portion of thestationary phase39 will be positioned in the fluid flow path between the first and second sensor electrodes. Finally, an end of each of thefirst sensor electrode37 and thesecond sensor electrode38 is in electrical communication with the measuringdevice20. Preferably, the suppressor anddetector16 is 21 mm×7.5 mm internal diameter. In a preferred aspect of the invention, the distance between theregeneration electrode30 and sensor electrode is about 7.95 mm. The distance betweenregeneration electrode32 andsensor electrode38 is about 11.8 mm. The distance betweensensor electrodes37 and38 is about 1.4 mm.

The system of the present invention may be used for detecting analyte ions comprising anions or cations. Moreover, a variety of mobile phases may be used. For cation analysis, preferred mobile phases include aqueous solutions of either hydrochloric acid, methanesulfonic acid or sulfuric acid. For anion analysis, preferred mobile phases include aqueous solutions of either sodium hydroxide or sodium carbonate/bicarbonate. Preferably, the mobile phase is aqueous and, therefore, no separate water-source is required. The operation of the suppressor anddetector16 will be described with reference to FIG. 2 for anion analysis and a mobile phase consisting of an aqueous solution of sodium hydroxide. As those of ordinary skill in the art will quickly appreciate, the invention may easily be adapted for cation analysis also.

To prepare the system for operation, the mobile phase should be flowed through the system and the power source turned on. Once the baseline created by the mobile phase has stabilized, the system is ready for ion analysis. A sample, which contains analyte anions to be detected and analyte counterions (e.g., cations), is injected atsample injector12 and flowed toanalytical column14 bypump11. The analyte anions are separated (or resolved) inanalytical column14 and then flowed with the mobile phase to suppressor anddetector16.

In anion analysis, thestationary phase39 in the suppressor anddetector16 is preferably ion exchange resin comprising exchangeable hydronium ions. The sample which contains the previously separated analyte anions fromanalytical column14 along with the analyte counter-cations are flowed with the mobile phase to the suppressor anddetector16. The analyte counter-cations are retained on thestationary phase39 by ion exchange with the hydronium ions. Thus, the analyte ions are converted to their relatively more conductive acid according to the following formula:

I⁺X⁻+stationary phase−H⁺=HX+stationary phase−I⁺

(where X⁻ comprises analyte anions selected from, for example, Cl, NO₂, Br, etc.; and I⁺ are analyte counterions selected from, for example, K⁺). Also, the sodium ions in the mobile phase may be retained on thestationary phase39 by ion exchange with the hydronium ions. Thus, the mobile phase is converted to the relatively non-conductive water according to the following formula:

NaOH+stationary phase−H⁺=H₂O+stationary phase−Na⁺

In addition to the foregoing reactions, a current is created acrossstationary phase39,first regeneration electrode30 andsecond regeneration electrode32 bypower source18. The water from the aqueous mobile phase undergoes electrolysis to form regenerating ions at thefirst regeneration electrode30 andsecond regeneration electrode32, respectively. In anion analysis, thefirst regeneration electrode30 is the anode at which regeneration ions consisting of hydronium ions are generated. Thesecond regeneration electrode32 is the cathode at which hydroxide ions are generated. As those skilled in the art will recognize, in cation analysis the polarity is reversed and the upstream regeneration electrode will be the cathode and the regenerating ions will comprise hydroxide ions.

In this embodiment, the regenerating hydronium ions generated at thefirst regeneration electrode30 are then flowed through thestationary phase39 thereby continuously regenerating thestationary phase39 by ion exchange of the regenerating hydronium ions with the retained sodium ions and analyte counter-cations according to the following formulas:

H⁺+stationary phase−Na⁺=stationary phase−H⁺+Na⁺

H⁺+stationary phase−I⁺=stationary phase−H⁺+I⁺

The sodium ions released from thestationary phase39 are flowed to thesecond regeneration electrode32 where they combine with the regeneration hydroxide ions to yield aqueous sodium hydroxide. If there are no analyte anions or analyte counter-cations flowing from the suppressor anddetector16, this aqueous sodium hydroxide may be flowed throughrecycling valve19 and back tomobile phase source10. In this fashion, a self-regenerating mobile phase is also provided. If, however, there are analyte anions or analyte counter-cations exiting the suppressor anddetector16 along with the aqueous sodium hydroxide, the fluid flow is preferably directed to waste. Preferably, the system will include a solvent recycling device, such as the ALLTECH SOLVENT RECYCLER 3000, which will sense the absence of analyte anions or analyte counter-cations and automatically direct the flow of the regenerated sodium hydroxide mobile phase tosource10. In contrast, if the solvent recycling device detects the presence of sample ions or counter-ions, it will direct the fluid flow to waste.

In a preferred embodiment of the invention, the analyte ions are detected while in the suppressor anddetector16. Still with reference to the anion analysis discussed above, there is a high concentration of hydronium ions proximate tosensor electrodes37 and38. The source of these hydronium ions are the regeneration hydronium ions generated atfirst regeneration electrode30 and the hydronium ions released from thestationary phase39 by ion exchange with the sodium ions and analyte counter-cations. Preferably, the concentration of hydronium ions is greater than the concentration of sodium ions or analyte counter-cations proximate the sensor electrodes. By optimizing the concentration of hydronium ions, the amount of sample ions in the acid form is likewise optimized, which leads to better detection sensitivity.

As discussed above, a current is applied across thestationary phase39 for generating the regeneration ions. When the analyte anions in their acid form are flowed to the sensor electrodes, a change in the current is detected by the sensor electrodes. This change in current, and the extent of the change, reflects the amount of analyte ion present in the suppressor anddetector16. Preferably, the change in current is detected by a measuringdevice20 and recorded.

In an alternate embodiment of the invention (not shown), the separate sensor electrodes may be omitted and the first andsecond regeneration electrodes30 and32 may also function as the sensor electrodes as previously described above. In yet another embodiment of the invention (not shown), one of the sensor electrodes may be omitted and one of the regeneration electrodes may perform the function of both a regeneration electrode and a sensor electrode as discussed above.

Another aspect of the invention using an ion-permeable ion exchange membrane is depicted in FIG.4. FIG. 4 is an exploded view of an alternative configuration for the suppressor and detector. Suppressors using ion exchange membranes having this general configuration (except for the sensor electrodes) are known in the art. Examples of these suppressors are disclosed in U.S. Pat. Nos. 5,248,426 and 5,352,360, the disclosure of which are hereby incorporated by reference. In the embodiment depicted in FIG. 4, afirst regeneration electrode130 and asecond regeneration electrode132 are provided. The electrodes may be constructed from the same materials as previously discussed. However, as those of ordinary skill in the art will appreciate, theelectrodes130 and132 preferably are not flow-through electrodes in this embodiment. First and secondion exchange membranes134 and135 are also provided. First and second ion exchange membranes preferably comprise exchangeable ions selected from the group consisting of hydronium and hydroxide ions. Positioned between ion exchangedmembranes134 and135 andelectrodes130 and132 are a first set ofspacers130aand132a,which define fluid flow paths providing fluid communication betweenelectrode130 and membrane134 andelectrode132 andmembrane135, respectively. Also, adjacent first and second ion exchange membranes are second set ofspacers140 and141, respectively, which define afluid flow path145. Thespacers130a,132a,140 and141 preferably may comprise a permeable, inert material such as a TEFLON membrane. Alternatively, the spacers may comprise an inert sheet constructed from MYLAR, PTFE, polypropylene or the like which has been cut to provide fluid communication betweenmembranes134 and135 and thefluid flow path145 as well as betweenelectrodes130 and132 andmembranes134 and135, respectively. Positioned inspacers140 and141 aresensor electrodes137 and138, respectively, which may be as previously described. Preferably, thesensor electrodes137 and138 are positioned at the downstream end offluid flow path145. As those skilled in the art will appreciate, the sensor electrodes will be positioned so that they are in fluid communication with thefluid flow path145. Also, in the configuration depicted in FIG. 4, in addition tofluid flow path145,fluid flow paths145aand145bare defined by the combination ofspacer130aand membrane134 andspacer132aandmembrane135, respectively.

In operation, the suppressor and detector depicted in FIG. 4 operates along the same general principles as previously discussed with respect to the embodiment depicted in FIGS. 1-3b.However, whereas the direction of current flow is generally parallel to the direction of fluid flow in the embodiment depicted in FIGS. 1-3b,the direction of current flow is generally perpendicular to the direction of fluid flow in the embodiment depicted in FIG.4. Thus, in anion analysis, for example, the sample comprising analyte ions (anions) and sample counterions along with an aqueous mobile phase comprising electrolyte counterions are flowed to suppressor anddetector116 andfluid flow path145. The water in the mobile phase undergoes electrolysis. In this embodiment,electrode130 may be the anode andelectrode132 may be the cathode. Thus, hydronium ions are generated atelectrode130 and hydroxide ions are generated at theelectrode132. As the analyte ions and mobile phase are flowed throughfluid flow path145, the analyte counterions and mobile phase electrolyte counterions are retained on themembranes134 and135 by ion exchange with hydronium ions. The hydronium ions, both from themembranes134 and135 and the electrolysis product of water, migrate tofluid flow path145 converting the analyte ions to their acid and the mobile phase to water. The analyte anions in their acid form may then be detected bysensor electrodes137 and138.

Additionally, the hydronium ions from the electrolysis will replace the retained electrolyte and sample counterions onmembranes134 and135 thereby regenerating these membranes. The released electrolyte counterions may then recombine with the hydroxide ions generated by the electrolysis atelectrode132 to regenerate the mobile phase, which may be reused as described previously.

Although thesensor electrodes137 and138 may be positioned in one of thefluid flow paths145,145aor145b,preferably, the sensor electrodes will be placed inpath145. Also, thesensor electrodes137 and138 are in electrical communication with a measuring device (not shown) for recording the detected analyte ions.

The devices and systems disclosed in U.S. Pat. Nos. 5,248,426 and 5,352,360 may be adapted for use according to yet another aspect of the invention. FIG. 4bshows a cross-section of a suppressor anddetector316 having the configuration of the suppressor and detector depicted in FIG. 4, except that the path of fluid flow through the suppressor and detector is modified. Theelectrodes330 and332,membranes334 and335 andspacers330a,332a,340 and341 may be as described with respect to FIG.4. Thesensor electrodes337 and338 are positioned in the fluid flow path345. Preferably, the sensor electrodes are positioned towards the downstream end of fluid flow path345. However, in this embodiment, the path of fluid flow is through fluid flow path345 and then back throughfluid flow paths345aand345bin a direction of flow opposite the direction of fluid flow through path345.

With reference to FIG. 4b, in anion analysis, for example, an aqueous mobile phase comprising electrolyte is flowed through fluid flow path345 tofluid flow paths345aand345bA sample comprising analyte anions and analyte counterions is flowed through fluid flow path345. The analyte counterions are retained onmembranes334 and335 by ion exchange with hydronium ions. Similarly, the mobile phase electrolytes are retained onmembranes334 and335 by ion exchange with hydronium ions. The released hydronium ions frommembranes334 and335 and the hydronium ions generated atelectrode330 from the electrolysis of water in the mobile phase combine with the analyte anions in the fluid flow path345 forming the acid of the analyte anions and converting the mobile phase to water. The analyte anions, in their acid form, are then detected in the fluid flow path345 bysensor electrodes337 and338, which are preferably in electrical communication with a measuring device (not shown).

The analyte anions (in their acid form) and water is then flowed tofluid flow paths345aand345b.This provides a continuous supply of water for the electrolysis. Also, the continuous supply of hydronium ions generated atelectrode330 replaces the retained sample and electrolyte counterions onmembranes334 and335, thereby continuously regenerating these membranes. The displaced sample and electrolyte counterions (cations) migrate towards electrode332 (where hydroxide ions are generated by the electrolysis) to flow path345band out of suppressor anddetector316. The effluent fromflow paths345aand345bmay be flowed to waste.

As those skilled in the art will appreciate, one of thespacers140 and141 (FIG. 4) orspacers340 and341 (FIG. 4b) may be eliminated. Thus, instead of two spacers, one spacer defining a fluid flow path145 (FIG. 4) or345 (FIG. 4b) may be used.

EXAMPLE 1

In this example, sample anions were analyzed according to a method of the invention using a suppressor and detector according to the embodiment of FIG.2. The following items were used. The analytical column was an ALLTECH ALLSEP anion column, 100×4.6 mm ID packed with methacrylate-based quaternary amine anion exchange resin. The mobile phase was aqueous 0.7 mM sodium bicarbonate/1.2 mM sodium carbonate. The mobile phase flow rate was 0.5 mL/min. The integrated suppressor and detector was packed with high capacity polystyrene divinylbenzene based sulfonated cation exchange resin (BIORAD AMINEX 50W-X12 200-400 mesh). The integrated suppressor and detector was a column 21×7.5 mm ID. The distance between the inlet regenerating electrode and the first sensor electrode was 7.95 mm. The distance between the second sensor electrode and the outlet regenerating electrode was 11.8 mm. The distance between the first and second sensor electrodes was 1.4 mm. The conductivity detector was an OAKTON 1000 series ¼ DIN conductivity and resistivity controller. The power source was a KENWOOD PR 32-1.2 A regulated DC power supply. The amount of current applied was 100 mA (corresponding voltage of 15 V).

FIG. 5 is the chromatogram for a sample anion mixture (100 μL). The following peaks correspond to the following anions: 1—flouride (10 ppm); 2—chloride (20 ppm); 3—nitrite (20 ppm); 4—bromide (20 ppm); 5—nitrate (20 ppm); 6—phosphate (30 ppm); and 7—sulfate (30 ppm).

EXAMPLE 2

In this example, the same equipment and conditions as in Example 1 were used. FIG. 6 is the chromatogram for a sample anion mixture with three repetitive injections of 100 μL each. The following peaks correspond to the following anions: 1—chloride (10 ppm); and 2—sulfate (10 ppm).

EXAMPLE 3

In this example, sample cations were analyzed according to a method of the invention shown in the embodiment of FIG.2. The following equipment and conditions were used. The analytical column was an ALLTECH Universal cation column, 100×4.6 mm ID, packed with silica coated with polybutadiene-maleic acid cation exchange resin. The mobile phase was aqueous 3.0 mM methane sulfonic acid. The mobile phase flow rate was 0.5 mL/min. The integrated suppressor and detector was packed with polystyrene divinyl benzene quaternary amine resin (BIORAD AMINEX AG-1-X8 100-200 mesh). The integrated suppressor and detector had the dimensions as set forth in Example 1. The conductivity detector was an OAKTON 1000 series ¼ DIN conductivity and resistivity controllers. A current of 200 mA was applied (corresponding voltage is 22 V).

FIG. 7 is a chromatogram for a sample cation mixture, 4 repetitive injections of 100μ mL each. The following peaks correspond to the following cations: 1—lithium (1 ppm); 2—potassium (6 ppm); and 3—magnesium (6 ppm).

It should be understood that the foregoing description of the preferred embodiments and the examples are not intended to limit the scope of the invention. The invention is defined by the claims and any equivalents.

Claims (14)

We claim:

1. A method of detecting analyte ions in an aqueous mobile phase comprising electrolyte using continuous electrochemical regeneration of a suppressor comprising:

(a) separating the analyte ions in a mobile phase comprising electrolyte;

(b) flowing the separated analyte ions and mobile phase through a suppressor comprising ion-exchange resin through which the mobile phase and analyte ions are flowed thereby suppressing the mobile phase electrolyte and at least partially exhausting the suppressor ion-exchange resin;

(c) flowing an aqueous liquid through the suppressor and applying an electrical potential across the suppressor ion-exchange resin during step (b) to electrolyze water and thereby generating regeneration ions selected from the group consisting of hydronium ions and hydroxide ions;

(d) flowing the regeneration ions through the at least partially exhausted suppressor ion exchange resin in substantially the same direction as the direction of liquid flow through the suppressor ion exchange resin during step (b): and

(e) detecting the analyte ions.

2. The method of claim1 wherein the aqueous liquid comprises the aqueous mobile phase.

3. The method of claim1 wherein the analyte ions comprise anions and the suppressor ion-exchange resin comprises hydronium ions.

4. The method of claim1 wherein the analyte ions comprise cations and the suppressor ion-exchange resin comprises hydroxide ions.

5. The method of claim1 wherein the analyte ions are detected during step (b).

6. The method of claim5 wherein the analyte ions comprise cations and the suppressor ion-exchange resin comprises anions.

7. The method of claim5 wherein the analyte ions comprise anions and the suppressor ion-exchange resin comprises cations.

8. The method of claim1 wherein the regeneration ions are flowed in substantially the same direction as the direction of the separated analyte ion flow through the suppressor ion exchange resin.

9. A method of detecting analyte ions in an aqueous mobile phase using continuous electrochemical regeneration of a suppressor comprising:

(a) separating the analyte ions;

(b) flowing the separated analyte ions through a suppressor comprising ion-exchange resin to suppress the mobile phase thereby at least partially exhausting the suppressor ion-exchange resin;

(c) flowing an aqueous liquid through the suppressor and applying an electrical potential across the suppressor ion-exchange resin during step (b) to electrolyze water and regenerate the at least partially exhausted suppressor ion-exchange resin; and

(d) detecting the analyte ions in the suppressor during step (b).

10. The method of claim9 wherein the analyte ions comprise anions and the suppressor ion-exchange resin comprises hydronium ions.

11. The method of claim9 wherein the analyte ions comprise cations and the suppressor ion-exchange resin comprises hydroxide ions.

12. The method of claim9 wherein in step (c) regeneration ions selected from the group consisting of hydronium ions and hydroxide ions are generated by the electrolysis of water, the regeneration ions being flowed across the at least partially exhausted ion exchange resin in substantially the same direction as the direction of liquid flow through the suppressor ion exchange resin.

13. The method of claim9 wherein in step (c) regeneration ions selected from the group consisting of hydronium ions and hydroxide ions are generated by the electrolysis of water, the regeneration ions being flowed across the at least partially exhausted ion exchange resin in substantially the same direction as the direction of separated analyte ion flow through the suppressor ion exchange resin.

14. A method of detecting analyte ions in an aqueous mobile phase comprising electrolyte using continuous electrochemical regeneration of a suppressor wherein the suppressor comprises a housing having suppressor ion exchange resin in direct contact with a pair of electrodes, the suppressor housing being a separate housing from an analytical column, the method comprising:

(a) separating the analyte ions in a mobile phase comprising electrolyte;

(b) flowing the separated analyte ions and mobile phase through the suppressor thereby suppressing the mobile phase electrolyte and at least partially exhausting the suppressor ion-exchange resin;

(c) flowing an aqueous liquid through the suppressor and applying an electrical potential across the suppressor ion-exchange resin during step (b) to electrolyze water and thereby generating regeneration ions selected from the group consisting of hydronium ions and hydroxide ions;

(d) flowing the regeneration ions through the at least partially exhausted suppressor ion exchange resin during step (b): and

(e) detecting the analyte ions in substantially the same direction as the direction of analyte ion flow through the suppressor ion exchange resin.

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